This section is home to Mid-IR Hybrid Lasers, a family of CW and pulsed solid-state bulk lasers operating in 1.64 to 5.2 μm wavelength range. Exploiting the synergy of IPG's proprietary capabilities, the Mid-IR Hybrid lasers are typically pumped by IPG's low-cost, reliable and efficient Er and Tm fiber lasers, and many are built with unique active crystals manufactured by IPG. Mid-IR Hybrid lasers span all modes of operation from CW to fs pulsed, and are complementary to Er, Tm and Yb Raman-shifted CW and pulsed IPG fiber laser families.

Mid-IR Applications

Materials Processing:

plastics cutting, welding, marking, drilling

forming of plastics

curing of coatings

Sensing and Imaging:

bioimaging

art imaging

hyperspectral imaging

thermography

tracking/ homing

night vision

LIDAR, Doppler scattering

Medical:

diagnostic, therapeutic, surgical;

breath analyzers

glucose monitoring

dermatology

cosmetic procedures

dental applications

Meteorology

Climatology

Astronomy

Communications

Spectroscopy:

molecular identification and dynamics

2D IR correlated spectroscopy

noninvasive nondestructive measurements

chemical agent and biomolecular sensing/ detection

Defense:

infrared countermeasures

target illumination and designation

covert communications

line-of-site communications

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Infrared Regions

Near IR extends from 0.7 µm to about 1.5-2.0 µm. The definition of the boundary between NIR and Mid IR depends on market/application/detection technology.

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Near IR and Mid IR Vibrational Bands

Near IR Vibrational Bands

From Metrohm “NIR Spectroscopy” monograph

Mid IR Vibrational Bands

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Existing Mid-IR Sources

• Quantum and Intraband Cascade Lasers

• Lead Salt and GaSb Lasers

• Gas Lasers (CO2,CO, HeNe, frequency doubled CO2)

• Chemical Lasers (HF, DF)

• DFG

• OPO/ OPA/ OPG

• Free Electron Lasers

• Bulk Solid State such as Er:YAG, Ho:YAG, Ho:YLF and other

• Fiber Lasers (Thulium, Holmium and Erbium doped)

• Many Mid-IR lasers don’t work at room temperature due to deactivation of energy accumulated in gain medium via non-radiative phonon assisted decay.

• Although existing Mid-IR sources already have found use in many applications, they have one or more disadvantages: limited power output, limited wavelength selection, limited range of tunability, low wall plug efficiency, large footprint, complex design, cooling, and high cost.

•The ground and first excited levels have the same spin, and therefore will have a relatively high cross-section of emission.

•Higher lying levels have spins that are lower than the ground and first excited levels, greatly mitigating the potential for significant excited state absorption at the pump or laser transition wavelengths.

•The orbital characteristics of the ground and first excited levels are different, and will experience a significant Franck-Condon shift between absorption and emission, resulting in broadband “dye-like” absorption and emission characteristics, suitable for a broadly tunable laser.

•SHG of Cr2+ ZnSe/S extends the coverage into Near IR (from 0.9 microns)

•OPOs extend coverage to longer wavelengths

•Research is under way to expand TM doped ZnSe/S coverage to longer wavelengths

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Mid-IR Gain Materials

•Cr2+ : ZnSe/S are gain materials of choice when one needs a compact fiber or diode pumped CW (or mode-locked) system with continuous tunability at 300K over 1.8-3.4 µm, output powers up to 20 W, and high (up to 70%) conversion efficiency.

Lasers based on Cr2+, Co2+ and Fe2+ : ZnSe/ZnS crystals are promising for spectroscopic, sensing, medical, and defense related applications, as well as for seeding, or pumping middle-infrared optical parametric oscillators.

Diode laser pumping of Mid-IR lasers can be used, provided pump diodes operate in required spectral range. However, diode pumps in this wavelength range have several disadvantages:

The diodes in 1.5-2 μm range have low power

Diodes have low brightness/poor beam mode

Wide spectral bandwidth and poor linewidth control

Er and Tm fiber lasers pumped by 1 μm diodes have wall plug efficiencies as good or better than direct diodes in this wavelength range, and can provide up to 200 W of spectrally pure diffraction-limited output. They provide the high power, high brightness, precise linewidth and linewidth control.

IPG Photonics offers Cr2+, Co2+ and Fe2+ diffusion-doped ZnSe/ZnS polycrystalline ceramic gain materials and saturable absorbers. IPG’s proprietary fabrication process allows low cost mass production of a large variety of iron and chromium doped ZnSe/ZnS crystals with low losses, uniform distribution of transition metal dopant, excellent reproducibility and reliability. The optical and spectroscopic characteristics of these crystals make them the gain materials of choice for compact and efficient laser sources operating in 1.8 to 6 microns range. Chromium and iron doped ZnSe/S lasers are promising for spectroscopy, sensing, medical and defense related applications, as well as for seeding or pumping middle-infrared optical parametric oscillators.

Mid IR Gain Media

Cr2+:ZnSe and Cr2+:ZnS Laser Active Materials

The unique combination of available pump sources (Er-fiber, Tm fiber, telecom or InP diodes, Er:YAG/YLF; Tm: YAG/YLF), technological (low cost ceramic material), optical and spectroscopic characteristics (ultrbroadband gain bandwidth, high st product and high absorption coefficients) make them the gain materials of choice when one needs a compact system with continuous tunability at 300 K over 1.8-3.4 mm, output powers up to 30 W and high (up to 70%) conversion efficiency.

Cr2+:ZnSe/S lasers are promising for spectroscopy, sensing, medical and defense related applications, as well as for seeding or pumping middle-infrared optical parametric oscillators.

IPG’s fabrication process allows low cost mass production of a large variety of diffusion-doped Cr2+:ZnSe/ZnS crystals with low losses, uniform distribution of chromium, good reproducibility and reliability.

Uniformly-doped 5 x 5 x 20 mm Cr:ZnSe Crystals

Output Characteristics of Cr:ZnSe/S Lasers Based on IPG's Gain Materials

These lasers are promising for spectroscopic, sensing, medical and defense related applications, as well as for seeding or pumping middle-infrared optical parametric oscillators.

IPG’s fabrication process allows low cost mass production of a large variety of diffusion-doped Fe²+:ZnSe/ZnS crystals with low losses, uniform distribution of iron, good reproducibility and reliability.

These lasers are used in numerous applications such as free-space communication systems, target designation, time-of-flight range finding, surgery, reflectometry and laser lidars.

IPG offers a large variety of diffusion-doped Co2+:ZnS, Co2+:ZnSe, Cr2+:ZnS and Cr2+:ZnSe polycrystals appropriate for Q-switching of the lasers operating in the 1.5-2.1 µm spectral range.

Samples of Cr2+:ZnS, Cr2+:ZnSe and Co2+:Zns Saturable Absorbers

Material Properties

Crystallographic

ZnS

ZnSe

Syngony

Cubic

Cubic

Symmetry Class

...

43 m

Mechanical

Density, g/cm3

4.09

5.27

Young Modulus, Pa

7.45×1010

7.03×1010

Poisson Ratio

0.28

0.28

Thermal

Thermal Expansion, deg C-1

6.5×10-6

7.6×10-6

Thermal Conductivity, W/(m deg C)

27.2

16

Specific Heat, J/(kg deg C)

0.515×103

0.339×103

Optical

Refractive Index at 1.0 µm

2.29

2.49

dn/dt, deg C-1

5.4×10-5

6.1×10-5

Transmission Range, µm

0.37 - 14

0.55 - 20

Q-Switching

Cr:ZnS

Cr:ZnSe

Co:ZnS

Co:ZnSe

σGSA (at 1.54 µm)

1.6×10-18

1.3×10-18

0.7×10-18

0.76×10-18

σESA (at 1.54 µm)

0

0.02×10-18

0.1×10-18

0.1×10-18

τGSA (at 1.54 µm)

5 µs

8 µs

200 µs

290 µs

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Fe doped ZnSe/S Passive Q-Switches

Fe2+:ZnSe, Fe2+:ZnS Passive Q-Switches

Fe2+:ZnSe and Fe2+:ZnS saturable absorbers (SA) are ideal materials for passive Q-switches of solid-state lasers operating in the spectral range of 2.5-4.0 µm.

These lasers (e.g. 3.0 µm Er:YAG/YSGG/YLF are used for pumping middle-infrared Optical Parametric Oscillators and for numerous medical and dental applications.

IPG’s fabrication process allows low cost mass production of a very large variety of diffusion-doped Fe2+:ZnSe/Zns crystals with low losses, uniform distribution of iron, good reproducibility and reliability.

Samples of Fe2+:ZnSe Single and Polycrystalline Saturable Absorbers

Crystal

Peak Coefficient Absorption, cm-1

Upper Level Lifetime at 300 K, µs

σGSA at 2.8 µm, 10-20 cm2

σgsa/σesa

σgsa/σYSGG

Fe:ZnSe

1-20

0.37

90

0

30

Fe:ZnS

1-20

<0.3

130

0

43

According to the criterion for saturable absorber Q-Switching

(where sQgsa and AQ are absorption cross section and area of the cavity mode at passive Q-switcher; sYSGG and AYSGG are emission cross section and area of the cavity mode at the gain element) Fe2+:ZnSe/S can be used as a saturable absorber Q-Switch for the Cr:Er:YSGG laser without intracavity focusing.

Output energies of 15 and 85 mJ were achieved in single and multipulse modes of operation, respectively. The combination of a high values of saturation cross-sectio, small saturation energy with good opto-mechanical (damage threshold - 2 J/cm2) and physical characteristics of ZnSe and ZnS hosts make Fe2+:ZnSe/S crystals an ideal material for passive Q-Switching of mid-infrared laser cavities.